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During discharging the electrochemical energy stored in the electrodes is converted to
electrical energy. The electrochemical reactions during discharging, results in water and
Lead Sulfate which coats both electrodes, recharging restores the situation.
While charging electrolysis of water decomposes, as a byproduct, water to its ingredients.
Oxygen gas is formed at the positive plate and Hydrogen gas at the negative plate.
Flooded Lead Acid Battery.
In Flooded, also called Wet , or Conventional Batteries, the oxygen and hydrogen gases
formed during charging are vented to the air. They therefore require periodic maintenance,
performed by authorized personnel, in order to check the sate of the battery and refill the
missing water, if needed.
Due to hydrogen’s explosive nature the batteries should be located in separate unmanned
and well vented rooms. These are generally used only in large installations, where long life
and cost /performance predominate, and where maintenance personnel is available.
Maintenance Free Valve Regulated (VRLA), Sealed Lead Acid ( LSA)
Batteries
In a Sealed Battery, the possibility of gas venting to the air is eliminated. The oxygen
diffuses through the separator from the positive plate to the negative plate, where it is
recombined with the hydrogen to form water. These batteries do not require water
refilling and are therefore called also Maintenance Free batteries.
To enable the possibility of pressure relief, mainly during overcharging, relief valves are
installed, to regulate to preset pressure level. Thus, UPS SLA batteries are frequently
called Valve Regulated Lead Acid (VRLA) type.
SLA batteries are considered dry type, generally spill proof and leak proof even in case of
container cracks or fractures. They can be located within the UPS as any other electrical
component.
Following features of the SLA type cause manufactures’ to prefer VRLA technology for
Uninterruptible Power Supply applications:
- Maintenance free, no water topping up is required during the whole service life.
- Non hazardous, have no restrictions for rail, road, sea or air transportation as part
- Rugged and vibration resistant. Can be shipped via parcel post or fast shipping
service.
- Non corrosive can be used for marine applications or wet environment.
- Can be located in any position (horizontal or vertical), enabling design flexibility.
- Allow location adjacent to each other or on top of each other (provided that weight
and venting are considered). Compact packaging in the enables using internal
batteries while increasing capacity and backup time.
- About 99% of the gas is recombined within the battery; practically no hydrogen is
emitted to the air, can be located in manned locations, where normal venting exists.
- The UPS can be designed to allow replacement or hot swapping of failed batteries
by the operators, or by local service people.
- High rate discharge ability. As requested for systems that provide high energies for
relatively short times.
- No memory effect. VRLA batteries retain their full charge in float condition during
lifetime.
| Operation and Features of Maintenance Free and Flooded UPS Power Supply Battery |
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